The present invention relates to a magnetic film forming apparatus, and in particular to a magnetic film forming apparatus capable of generating a uniform magnetic field to form a magnetic film with an excellent magnetic characteristic.
As a method of forming a magnetic film in which the magnetic moment is arranged in one direction, an in-magnetic-field sputtering-method is known according this method, a magnetic film is formed while orienting the magnetization direction of film forming particles by applying a magnetic field to the film forming particles in one direction.
In a conventional magnetic film forming apparatus for forming a magnetic film by using the in-magnetic-field sputtering method disclosed, for example, in Japanese Patent Application Laid-Open Hei-7 254603 and Japanese Patent Application Laid-Open Hei-8 30780. A substrate on which a magnetic film is formed is placed opposite to a target in a sputtering chamber. The substrate is held by a substrate holder, and further kept in parallel to the target at a predetermined distance by internal fittings. Moreover, two permanent magnets are provided on the substrate holder. In the upper part of the sputtering chamber, a guide bar of a heater is attached to the sputtering chamber via an o-ring. In the aperture part in the lower portion of the sputtering chamber, a target electrode is fixed to the sputtering chamber via an insulation member, and the target is attached to the target electrode. Also, an earth shield is provided around and apart from the target with a constant gap distance.
The magnetic film forming apparatus generates plasma by applying voltage to the target from an RF (radio wave) power source via the target electrode, and ions in the generated plasma make sputtering-particles emit from the target. The sputtering-particles emit from the target arrive at the surface of the substrate, and form a magnetic film on the surface. Since the magnetic field near around the substrate is applied by the permanent magnets provided on the substrate holder, the magnetization direction of the sputtering-particles in the formed magnetic film is oriented in the same direction.
In the space near the substrate in this magnetic film forming apparatus, two bar-shaped permanent magnets are arranged at the both sides of the substrate in parallel to the substrate. Moreover, the substrate is fixed in the center of the space between the two permanent magnets, and an orientation flat is provided on the substrate so it will not rotate.
However, in the above-mentioned composition of this conventional magnetic film forming apparatus, in both the top portions of the substrate in the longitudinal direction, the generated magnetic field is not straight between the two permanent magnets, but instead expands somewhat toward the outside of the substrate. Therefore, to decrease the expansion of the magnetic field, a pair of auxiliary magnets are provided opposite to each other at places between pairs of end portions of the two permanent magnets arranged in parallel. Otherwise two auxiliary magnets are attached to the two ends of the respective permanent magnet. Thus, in a comparatively wide region between the two permanent magnets, a magnetic field perpendicular to those magnets can be realized.
Such a composition or arrangement of the main permanent magnets and the auxiliary magnets is complicated, and has been difficult to optimize. Furthermore, to reduce the variance in the distribution of etching which is performed on the surface of the substrate in advance and in the property of a formed magnetic film, it is desirable to set a large distance L between the two permanent magnets, which in turn requires a larger length for the two magnets. Moreover, the optimal arrangement for the magnets of given sizes is uniquely determined. Accordingly, if the distance L between the two permanent magnets is changed to meet a requirement to change the strength or the distribution of the magnetic field, it becomes difficult to obtain the optimal arrangement of the magnets again by adjusting the positions of the auxiliary magnets.